If you are using the relay shield from elecrow, this is the procedure to make your project:
- upload the sketch relay_shield from the librairy
- scan your NFC tag with the Serial monitor open. It should answer you the ID of the tag
- add the ID here instead of the cross : String NFC_KEY_1 = "XXXXXXXXXXXXXX";
- reupload the modified sketch and re-scan your tag
If you have some trouble, just send me the ID, I will make the change with the sketch.